The present invention relates to a wiper ring to be mounted to an end portion of a nut of a ball screw and also relates to a ball screw provided with such wiper ring.
Japanese Utility Model Laid-open Publication No. HEI 6-6795 disclosed such a wiper ring, in which one end side portion or entire portion of a wiper ring is divided into a plurality of segments or blocks in a circumferential direction thereof, and each of the segments is pressed towards radially center side by means of spring to thereby improve tightness between an inner peripheral portion of the wiper ring and a screw shaft disposed inside therein.
In such known art, in the structure in which only the one end side portion of the wiper ring is divided into a plurality of segments or blocks, there is usually formed a cutout portion, called xe2x80x9cbias-cutxe2x80x9d, at one portion of the wiper ring in its circumferential direction for separating the same. However, in an arrangement in which such wiper ring is mounted to a screw shaft, the bias-cut portion is widened (opened) and the inner peripheral portion of the wiper ring is deformed unwillingly in form of non-circular shape, and for this reason, at a portion opposite to the bias-cut forming portion of the wiper ring, the segment is closely contacted to the screw shaft. However, on the side of the bias-cut forming portion, the tightness of the segment to the screw shaft is made worse. As a result, sealing performance of the ball screw may be made different at various portions, thus being inconvenient.
On the other hand, the case where the entire portion of the wiper ring is divided into a plurality of segments or blocks will cause the following defective.
In such structure, when a gap is formed between adjacent two segments in the circumferential direction thereof, the gap may be widened when the segments are shifted. In such occasion, foreign material or like may easily invade and lubricant may easily leak through the widened gap. On the contrary, when the segments are contacted to each other in order to eliminate such gap, the movement of the respective segment towards the radially central portion of the segment due to such mutual contacting will be limited, which results in degradation of tightness between the segments and the screw shaft and deterioration of the sealing performance. Furthermore, in a case where any foreign material is clogged between the segment and the screw shaft, the segment is displaced towards the radially outer peripheral side against the force of the spring pressing the segment, and hence, the inner peripheral portion of the segment is separated from the screw shaft, thus deteriorating the sealing performance and hence being defective.
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a wiper ring and a ball screw provided with the wiper ring, by which sealing performance of a screw shaft with respect to segments of the wiper ring can be enhanced.
The above and other objects can be achieved according to the present invention by providing, in one aspect, a wiper ring to be applied to a screw unit having a shaft member comprising:
a plurality of segments each constituted as independent element having a seal portion to be contacted to the shaft member;
support shafts extending in an axial direction of the shaft member so as to correspond to the segments, respectively, the segments being arranged in a circumferential direction of the shaft member to be rotatable about the support shafts, the support shafts being connected to each other through support members so as to limit relative movement of the respective support shafts; and
a spring member for urging the segments arranged circumferential direction of the shaft member so as to be directed towards radially central side of the shaft member.
According to the wiper ring of this aspect, the respective segments are deformed in their attitudes so as to closely contact the shaft member such as screw shaft of the ball screw unit while being pressed towards the central side of the screw member by means of spring and rotating about the support shafts such as pins. Accordingly, the respective segments can be well contacted to the shaft member, and the improved sealing performance can be realized at any circumferential position.
Further, the support shafts of the respective segments are mutually connected to thereby limit or restrict the relative movement of the support shafts, so that the movement of the segments in the circumferential and radial directions can be properly limited. Therefore, the biting of foreign material in a widened gap between the segments in the circumferential direction can be prevented, the leakage of lubricant can be also prevented, and the degradation of the sealing performance due to the movement of the segments in the radially outer peripheral direction can be further prevented.
Further, in the present invention, the state, that the support shafts as rotational centers of the respective segments are connected to each other, means that the support shafts are connected to each other through members different from the segments or through the segments themselves to thereby restrict the relative movement therebetween. The support shafts may be constituted independently from the segment, or segment itself is utilized as support shaft.
In a preferred embodiment of this aspect, the support member is a support ring formed as a member independent from the segments and the support shafts are connected to each other through the support ring.
In this example, the respective segments are supported by the support ring to be rotatable about the support shafts such as pins. The support ring may be separated at one portion in its circumferential direction, and in such case, since the cut portion corresponding to the bias-cut in the conventional structure of the wiper ring is formed on the support ring, the wiper ring can be entirely deformed and the segments can be surely urged against the shaft member by the spring member.
Furthermore, according to this aspect, (Nxe2x88x922) segments in the plural segments (N: total number thereof are formed with the support shafts and hole portions for receiving the support shafts in an arrangement shifted in the circumferential direction of the shaft member, either one of remaining two (2) segments is provided with the support shaft and another one of the remaining two segments being formed with the hole portion, the segments being connected to each other by fitting the support shafts to the hole portions of the adjacent two segments in the circumferential direction in a manner that the remaining two segments are unconnected.
According to this example, the respective adjacent segments can be supported to be rotatable about the support shafts and the respective support shafts can be connected through the segments. Therefore, no connection is made between two segments, so that the cut (separated) portion, corresponding to the conventional bias-cut, is formed and the wiper ring can be entirely deformed. Thus, the segments can be surely urged against the shaft member by the spring member.
Furthermore, it may be possible that each of the segments comprises a segment body having the seal portion and a support plate arranged in a manner shifted in the circumferential direction with respect to the segment body, either one of the support plate and the segment body is formed with the support shaft and another one thereof is formed with the hole portion.
In this example, since the support plate extends behind a slit formed between the segment bodies, so that the inside and outside portions of the wiper ring are not communicated through the slit, and hence, the invasion of foreign material can be prevented as well as leakage of the lubricant.
In another aspect of the present invention, there is also provided a wiper ring to be applied to a screw unit having a shaft member comprising:
a support ring;
a plurality of segments each having a seal portion to be contacted to the shaft member, the segments being arranged on one side of the support ring in a circumferential direction of the support ring and connected to each other to be rotatable about a predetermined support shaft with respect to the support ring; and
a spring member for urging the segments arranged in the circumferential direction of the support ring towards radially central side of the support ring.
According to the wiper ring of this aspect, substantially the identical advantageous effects to those mentioned above will be achieved. That is, since the respective segments can be supported by the support ring to be rotatable about the support shafts such as pins, the respective segments are deformed in their attitudes so as to closely contact the shaft member such as screw shaft of the ball screw unit while being pressed towards the central side of the screw member by means of spring and rotating about the support shafts such as pins. Accordingly, the respective segments can be well contacted to the shaft member, and the improved sealing performance can be realized at any circumferential position.
Further, the support shafts of the respective segments are mutually connected through the support ring to thereby limit or restrict the relative movement of the support shafts, so that the movement of the segments in the circumferential and radial directions can be properly limited. Therefore, the biting of foreign material in a widened gap between the segments in the circumferential direction can be prevented, the leakage of lubricant can be also prevented, and the degradation of the sealing performance due to the movement of the segments in the radially outer peripheral direction can be further prevented.
The support ring may be separated at its one portion in the circumferential direction, and in such case, the cut (separated) portion, corresponding to the conventional bias-cut, is formed on the support ring, so that the wiper ring can be entirely deformed. Thus, the segments can be surely urged against the shaft member by the spring member.
In this aspect, a slit may be formed between adjacent segments when the segments are connected to the support ring.
In a further aspect, there is provided a wiper ring to be applied to a screw unit having a shaft member comprising:
a plurality of segments each having a seal portion to be contacted to the shaft member, the segments being arranged in a circumferential direction of the shaft member; and
a spring member for urging the segments arranged in the circumferential direction of the shaft member in the radially central direction of the shaft member,
wherein (Nxe2x88x922) segments in the plural segments (N: total number thereof) are formed with support shafts extending in an axial direction of the shaft member and hole portions for receiving the support shafts in an arrangement shifted in the circumferential direction of the shaft member, either one of remaining two segments is provided with the support shaft and another one of the remaining two segments being formed with the hole portion, the segments being connected to each other by fitting the support shafts to the hole portions of the adjacent two segments in the circumferential direction in a manner that the remaining two segments are unconnected.
According to the wiper ring of this aspect, the respective adjacent segments are supported to be rotatable about the support shafts such as pins, so that the respective segments are deformed in their attitudes so as to closely contact the shaft member such as screw shaft of the ball screw unit while being pressed towards the central side of the screw member by means of spring and rotating about the support shafts. Accordingly, the respective segments can be well contacted to the shaft member, and the improved sealing performance can be realized at any circumferential position.
Further, the support shafts of the respective segments are mutually connected to thereby limit or restrict the relative movement of the support shafts, so that the movement of the segments in the circumferential and radial directions can be properly limited. Therefore, the biting of foreign material in a widened gap between the segments in the circumferential direction can be prevented, the leakage of lubricant can be also prevented, and the degradation of the sealing performance due to the movement of the segments in the radially outer peripheral direction can be further prevented.
Furthermore, the connection between the adjacent two segments is interrupted, the cut (separated) portion, corresponding to the conventional bias-cut, is formed on the support ring, so that the wiper ring can be entirely deformed. Thus, the segments can be surely urged against the shaft member by the spring member.
In this aspect, a slit is formed between adjacent segments when the respective segments are connected.
In still further aspects of the present invention, there are provided ball screw or ball screw units each comprising:
a screw shaft;
a number of rolling members to be applied to the screw shaft;
a nut mounted to the screw shaft through the rolling members; and
a wiper ring mounted to at least one axial end portion of the nut, the wiper ring comprising the elements or members mentioned above with respect to first, another and further aspects of the present invention.
According to the ball screw (unit) utilizing the wiper ring of the above aspects, the wiper ring is mounted to at least one end portions of the nut, so that the durability of the nut against the foreign material or like can be achieved with the improved sealing performance of the wiper ring.
Further, it is to be noted that the nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.